Biodiversity Loss — Practice · Grade 12 Science

Chapter: Conservation, Systems & Environmental Design

What this practice covers

By the end of Biodiversity Loss you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: biodiversity, extinction, habitat fragmentation, invasive species, ecosystem services.

Problem 1

Which listed activity directly removes habitat and separates remaining habitat patches?
  1. Scientists collecting a few specimens for study
  2. Natural predators hunting their usual prey
  3. Zoos keeping some animals in captivity
  4. Habitat loss and fragmentation from clearing and dividing land
Answer and explanation

Habitat loss and fragmentation from clearing and dividing land

Clearing and dividing land can reduce available habitat and connectivity. The relative importance of threats varies among ecosystems and requires evidence.

Problem 2

An invasive species is best described as
  1. a non-native species that spreads rapidly in a new area and harms native species
  2. any large predator at the top of a food chain
  3. a native species that has lived in an ecosystem for thousands of years
  4. any species that is currently close to extinction
Answer and explanation

a non-native species that spreads rapidly in a new area and harms native species

Invasive species are non-natives that, lacking natural predators or competitors in the new range, spread out of control and damage native populations.

Problem 3

A coastal wetland covering 500 hectares is drained and developed until only 75 hectares remain. What percentage of the original wetland habitat was lost?
Answer and explanation

85 %

Area lost = 500 - 75 = 425 hectares; 425 ÷ 500 = 0.85, or 85% of the wetland lost.

Problem 4

Describe two ecosystem services that healthy, biodiverse ecosystems provide to people, and explain why losing biodiversity puts them at risk.
Answer and explanation

Examples include pollination of crops by insects, filtering and cleaning of water by wetlands and forests, fertile soil built by soil organisms, flood control, and climate regulation. These services depend on many interacting species; as biodiversity declines, the organisms that perform them are lost and the services weaken or fail, directly harming the food, water, and protection people rely on.

Problem 5

Scientists estimate that species are going extinct roughly 100 to 1,000 times faster than the natural 'background' rate. Why does this concern them?
  1. Because a higher extinction rate must mean the number of species is increasing
  2. Because extinctions at this pace outrun the rate at which evolution produces new species, so total biodiversity is falling and lost species can never be recovered
  3. Because faster extinction means new species also appear faster, keeping biodiversity constant
  4. Because extinction has never happened before in Earth's history
Answer and explanation

Because extinctions at this pace outrun the rate at which evolution produces new species, so total biodiversity is falling and lost species can never be recovered

Extinction is permanent, and losing species far faster than new ones evolve means biodiversity is steadily and irreversibly declining.

Problem 6

How can fragmentation threaten a population without reducing total habitat area immediately? Show the reasoning, not just the conclusion.
Hints

Absence of detection is not proof of absence.

Answer and explanation

It can restrict movement, gene flow and access to resources and increase edge effects.

Problem 7

What evidence supports a conservation outcome beyond a publicity claim?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Comparable abundance, reproduction, habitat or functional measures with methods, baseline and uncertainty disclosed.

Problem 8

Trend interpretation requires matched observation conditionsTrend interpretation requires matched observation conditionsObserved individuals04080120123Survey year indexMatched-effort illustrationChanging-effort illustration
Synthetic count examples with deliberately different possible observation processes; not a correction to an actual field record.
Interpret the supplied visual. What records are essential alongside a count series?
Answer and explanation

Survey area, method, effort, timing, observer/detection conditions and relevant uncertainty.

Observed abundance depends on true population, sampled extent, effort and detectability. A declining count may signal ecological loss, but an observation model is needed to separate that from reduced survey effort or changed visibility. The two hypothetical curves are reminders of this ambiguity, not proof that any particular real decline is only a measurement artifact. Preserve all source labels and compare repeated standardized monitoring or an appropriate detection-adjusted analysis.

Survey area, method, effort, timing, observer/detection conditions and relevant uncertainty.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 9

A population estimate falls from 500 to 350 under comparable methods. Find percent decline. Explain why this does not prove global extinction or identify a unique cause.
Answer and explanation

Decline=(500−350)/500=30%. Living individuals remain in the defined population, and the record alone cannot distinguish survival, reproduction, movement or the pressures affecting them.

Decline=(500−350)/500=30%.

Living individuals remain in the defined population, and the record alone cannot distinguish survival, reproduction, movement or the pressures affecting them.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 10

OpenSciEd graph titled observed Masai giraffe numbers, 1977–2015 in Kenya, with a high early peak, lower later counts and sharp fluctuations; its displayed data credit names IUCN and Muller et al. (2018).
Preserve the source title and observed Masai giraffe/Kenya scope. The drawn trace does not supply a complete annual 1977–2015 table. Historical Masai giraffe observations in Kenya · OpenSciEd · 7.5 Ecosystem Dynamics, Lesson 10 graph; data source retained in image, source, CC BY 4.0. Figure excerpt rendered from the PDF and resized for the web.
Describe a broad pattern without inventing exact missing annual values. Explain why this source alone neither measures all global giraffes nor establishes a unique cause of decline.
Answer and explanation

The displayed observed counts fluctuate, with an early high peak and many lower later counts. It is a Kenya-scoped observed-count graph, not a global census. Search effort, coverage, detection and demographic/pressure evidence are needed to interpret actual abundance and causes. The title’s interval must not be used to fabricate unplotted exact annual values.

Read source labels, scope, axes and intentional omissions.

Use the complete local explanation to draw a justified mechanism or calculate a supported quantity.

State what is observed, what is assumed and what evidence remains needed.

Response criteria

  • Interpret the source labels, units and scope accurately.
  • Explain the relevant mechanism with a labeled model or supported calculation.
  • Identify a meaningful assumption, uncertainty or missing comparison.

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